1. Field of the Invention
The application relates to a method utilized in a wireless communication system and a communication device thereof, and more particularly, to a method of handling component carrier activation and deactivation in a wireless communication system and a related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as user equipments (UEs).
Architecture of the radio interface protocol of the LTE system includes three layers: the Physical Layer (L1), the Data Link Layer (L2), and the Network Layer (L3), wherein a control plane of L3 is a Radio Resource Control (RRC) layer, and L2 is further divided into a Packet Data Convergence Protocol (PDCP) layer, a Radio Link Control (RLC) layer and a Medium Access Control (MAC) layer.
Toward advanced high-speed wireless communication system, such as transmitting data in a higher peak data rate, LTE-Advanced system is standardized by the 3rd Generation Partnership Project (3GPP) as an enhancement of LTE system. LTE-Advanced system targets faster switching between power states, improves performance at the cell edge, and includes subjects, such as bandwidth extension, coordinated multipoint transmission/reception (COMP), uplink multiple input multiple output (MIMO), etc.
For bandwidth extension, carrier aggregation is introduced to the LTE-Advanced system for extension to wider bandwidth, where two or more component carriers or cells are aggregated, for supporting wider transmission bandwidths (for example up to 100 MHz) and for spectrum aggregation. According to carrier aggregation capability, multiple component carriers are aggregated into overall wider bandwidth, where the UE can establish multiple links corresponding to the multiple component carriers for simultaneously receiving and/or transmitting.
In the LTE-Advanced system, a UE in a radio resource control (RRC) connected state is configured with multiple component carriers to communicate with the network (i.e. an eNB). Since the UE may not need to use all of the configured component carrier cc#1-cc#m, only some of the multiple component carriers are activated. Generally, the eNB activates or deactivates a component carrier by sending a signalling (e.g. a MAC control element) to the UE. In addition, the UE starts a deactivation timer for the component carrier when the component carrier is activated, wherein the component carrier is deactivated when the deactivation timer expires. In other words, the deactivation timer provides a period of time for component carrier activation. Please note that, when the component carrier is deactivated, the UE does not need to receive or transmit the corresponding PDCCH or physical downlink shared channel (PDSCH), nor require to perform channel quality indicator (CQI) measurement on the component carrier. Conversely, when the component carrier is activated, the UE shall receive or transmit PDSCH and PDCCH, and is expected to be able to perform CQI measurement.
Based on the abovementioned description, the applicant noticed a problem related to deactivation of component carrier(s), and several scenarios are described as follows.
In the first scenario, a retransmission of a Hybrid Automatic Repeat Request (HARQ) process performed on an activated component carrier is not finished when UE receives a signalling (e.g., MAC control element) which commands the UE to deactivate the component carrier or a deactivation timer corresponding to the activated component carrier expires. More specifically, for uplink transmission, the UE receives Physical Downlink Control Channel (PDCCH) or Physical Hybrid ARQ Indicator channel (PHICH) for a HARQ feedback (e.g. HARQ positive acknowledgement (ACK) or negative acknowledgement (NACK)) if an uplink grant for a pending HARQ process retransmission occurs or there is data in a HARQ buffer corresponding to the HARQ process. However, when the UE receives HARQ ACK/NACK on the activated component carrier, the UE may not be able to finish a HARQ process retransmission triggered according to the HARQ ACK/NACK before deactivation of the component carrier (e.g. due to receiving a deactivation MAC command or expiry of the deactivation timer), causing HARQ process retransmission loss. On the other hand, for downlink transmission, the UE receives PDCCH/PDSCH on the activated component carrier, and starts HARQ round trip time (RTT) timer for the component carrier. The HARQ RU timer means the minimum amount of subframes before a downlink HARQ retransmission is expected by the UE. However, the component carrier may be deactivated during duration of the HARQ RTT timer. Therefore, the downlink HARQ process retransmission cannot be received by the UE due to deactivation of the component carrier, after the HARQ RTT timer expires, causing HARQ retransmission loss. Note that, the HARQ process shall be well-known in the art, so the detailed description for the HARQ functionality and operation are omitted herein.
In the second scenario, when the UE has new uplink data to transmit but has no uplink resource available, the UE triggers a Scheduling Request (SR) procedure to request the network to allocate the uplink resource. Note that, when the SR procedure is triggered, the UE considers the SR procedure as pending until the uplink resource is received. In addition, the uplink resource may be allocated in any of the activated component carriers. However, the uplink resource may not be received before deactivation of the component carrier (e.g. due to receiving a deactivation command or expiry of the deactivation timer corresponding to the activated component carrier). Thus, the UE loses the uplink opportunity to perform uplink data transmission.
In the third scenario, a discontinuous reception (DRX) operation allows the UE to monitor signaling of the PDCCH only during certain configured periods (e.g. called DRX active time) in order to save UE power. However, the component carrier may be deactivated (e.g. due to receiving a deactivation command or expiry of the deactivation timer) during the DRX active time, and thereby the UE can not monitor the PDCCH during the DRX active time, causing the time for monitoring PDCCH decreasing.
In the fourth scenario, the UE performs a random access procedure for uplink synchronization or for initial cell access. During the random access procedure, a contention resolution message (or a random access response message) of the random access procedure may be allocated in any of the activated component carriers. However, the UE may not receive the contention resolution message (or a random access response message) before deactivation of the component carrier (e.g. due to receiving a deactivation command or expiry of the deactivation timer). Thus, the random access procedure cannot be finished, causing uplink synchronization and initial cell access failure.
In the fifth scenario, a PDCCH assignment for a component carrier may be transmitted on the same or different component carrier. That is, a first component carrier may receive a PDCCH assignment for a second component carrier (called cross component carrier scheduling). However, the first component carrier may be deactivated (e.g., due to receiving a deactivation command or expiry of the deactivation timer), and thereby cannot receive the PDCCH assignment for the second component carrier, causing cross component carrier scheduling failure.
In the sixth scenario, UE may still have data in near future when the deactivation timer is going to be expired. For example, the UE receives a PDCCH or PDSCH assignment indicating a new downlink/uplink transmission on an activated component carrier, and thereby knows that there is an upcoming data for reception/transmission. However, the UE is unable to receive/transmit the upcoming data due to deactivation of the component carrier (e.g. due to receiving a deactivation command or expiry of the deactivation timer), causing downlink/uplink transmission unfinished or failure.